1. Field of the Invention
The present invention relates to a compact antenna for use on vehicles and the like, and a manufacturing method therefor.
2. Description of the Related Art
Keyless entry systems are already available for use on vehicles enabling their user to remotely lock or unlock the doors of a vehicle with a signal transmitted from a wireless apparatus carried by the user. In such a keyless entry system, a door handle of the vehicle is provided with a compact antenna electromagnetically coupled to an antenna provided on the wireless apparatus carried by the user to transmit and receive necessary signals. As this compact antenna, one comprising a rod-shaped ferrite core around which a coil is wound is commonly used because of its low cost.
However, since ferrite is a brittle material, a compact antenna made of ferrite, when used in a keyless entry system, is likely to be easily cracked or chipped by the bending stress it is subjected to every time the door handle is operated, with the result that the communication performance of the compact antenna is susceptible to deterioration. This is particularly true of compact antennas using a rod-shaped ferrite core, which is subjected to heavy bending when exposed to external force.
It is proposed to add elasticity to antennas for more common use on vehicles for receiving radio waves or the like by inserting a plurality of unit cores into a hollow in the coil. However, in this kind of antenna for use on vehicles, each unit core is held only by the elasticity of the coil and moves independent of the coil, and the set spacing between the unit cores varies with the deformation of the coil, with the consequence that the communication performance of the coil is unstable and, moreover, any major external force is likely to subject the coil to plastic deformation, which means inadequate durability.
This kind of antenna for use on vehicles is manufactured by successively inserting a plurality of unit cores into the hollow in a coil, which is wound tightly and closed at one otherwise open end, from the other open end, thereby extending the tightly wound coil into a sparsely wound state, and engaging that other open end of the coil with the last inserted unit core. Since the plurality of unit coils formed independent of the coil are successively inserted into the hollow in the coil, the insertion of the unit cores into the coil takes a long time, tending to push up the cost of the antenna.
An object of the present invention, attempted to eliminate these shortcomings of the prior art, is to provide a compact antenna not easily broken by external force, stable in communication performance and excelling in durability, and a method for manufacturing such a compact antenna at low cost.
In order to solve the problems noted above, according to the invention, there is provided a compact antenna comprising a plurality of unit cores, linking members for linking external faces of the unit cores, and a coil wound around the plurality of unit cores, wherein the linking members are bendably arranged between the unit cores.
This configuration of linking external faces of the plurality of unit cores by linking members and arranging the linking members to be bendable between the unit cores serves to protect the unit cores from destruction and ensures stable communication performance for a long period because any external force would bend the linking members and prevent any major stress from arising in the unit cores. Also, as the unit cores are linked by the linking members, even if any external force deforms the compact antenna, the set spacing between the unit cores will remain unchanged to enable stable communication performance to be maintained. Moreover, as the unit cores are linked by the linking members, the deformation of the coil is regulated by the linked assembly of the unit cores, and deterioration in communication performance due to coil deformation can also be prevented. Furthermore, the arrangement of the linking members on the external faces of the plurality of unit cores enables the compact antenna to be formed in a planar shape, making it possible to provide a thin compact antenna.
The compact antenna may also have an arrangement in which the linking members in the above-described configuration are formed of elastic bodies.
The formation of the linking members of elastic bodies eliminates the need to form elastically deformable portions in the linking members, which are indispensable for rigid linking members, and the configuration of the linking members can be simplified with corresponding saving in the manufacturing cost of the compact antenna.
At the same time, regarding a compact antenna manufacturing method, the present invention provides a configuration comprising a step of winding a coil, a step of linking a plurality of unit cores by linking members, and a step of inserting into a hollow in the coil the plurality of unit cores linked by the linking members.
Thus, as the insertion of the plurality of unit cores linked by the linking members into a hollow in the coil makes it possible to insert a plurality of unit cores into a coil in a single process, the time required for inserting unit cores into the coil can be made shorter than inserting a plurality of unit cores one by one into a coil, resulting in corresponding saving in the compact antenna manufacturing cost.
A compact antenna manufacturing method according to another aspect of the invention comprises a step of linking a plurality of unit cores by linking members and a step of winding a coil around a linked assembly of the linking members and the plurality of unit cores linked to them.
The winding of the coil around the linked assembly of the linking members and the plurality of unit cores linked to them after linking the plurality of unit cores by the linking members as described above can make the integration of the coil with the linked assembly easier than inserting the unit cores and the linking members into the hollow in the wound coil, resulting in corresponding saving in the compact antenna manufacturing cost.